The invention relates generally to electronic circuits and, in particular, to current mirror devices and methods for operating a current mirror device.
Current mirrors are widely used in analog integrated circuits. A current mirror is a transistor-based circuit that copies or “mirrors” a reference current in one active device by controlling a current in another active device. A current mirror may function as either a current source or a current sink. Current mirrors are often used to provide bias currents or to serve as an active load.
A basic diode configuration for a current mirror has an optimized input headroom and output headroom, but at the sacrifice of output resistance. A stacked configuration may result in an improved output resistance in comparison with the basic diode configuration and similar to increasing the transistor channel length in the basic diode configuration, but at the sacrifice of input headroom and output headroom. A cascode configuration for a current mirror has an output resistance that is appreciably higher than the output resistance of the basic diode configuration or the stacked configuration, but at the sacrifice of input headroom and output headroom. A swing-enhanced cascode configuration has an improved output resistance, input headroom, and output headroom in comparison with the cascode configuration, but requires an additional branch of biasing current. A self-biased swing-enhanced cascode configuration eliminates the additional branch of biasing current needed in the swing-enhanced cascode configuration, but at the sacrifice of input headroom due to the introduction of a resistor at the input node.
Improved current mirror devices and methods for operating a current mirror device are needed.